A review on plasmonic-based heterojunction photocatalysts for degradation of organic pollutants in wastewater

Abstract

Organic pollutants in wastewater are the biggest problem facing the world today due to population growth, rapid increase in industrialization, urbanization, and technological advancement. There have been numerous attempts to use conventional wastewater treatment techniques to address the issue of worldwide water contamination. However, conventional wastewater treatment has a number of shortcomings, including high operating costs, low efficiency, difficult preparation, fast recombination of charge carriers, generation of secondary waste, and limited light absorption. Therefore, plasmonic-based heterojunction photocatalysts have attracted much attention as a promising method to reduce organic pollutant problems in water due to their excellent efficiency, low operating cost, ease of fabrication, and environmental friendliness. In addition, plasmonic-based heterojunction photocatalysts contain a local surface plasmon resonance that enhances the performance of photocatalysts by improving light absorption and separation of photoexcited charge carriers. This review summarizes the major plasmonic effects in photocatalysts, including hot electron, local field effect, and photothermal effect, and explains the plasmonic-based heterojunction photocatalysts with five junction systems for the degradation of pollutants. Recent work on the development of plasmonic-based heterojunction photocatalysts for the degradation of various organic pollutants in wastewater is also discussed. Lastly, the conclusions and challenges are briefly described and the direction of future development of heterojunction photocatalysts with plasmonic materials is explored. This review could serve as a guide for the understanding, investigation, and construction of plasmonic-based heterojunction photocatalysts for various organic pollutants degradation. Graphical abstract Herein, the plasmonic effects in photocatalysts, such as hot electrons, local field effect, and photothermal effect, as well as the plasmonic-based heterojunction photocatalysts with five junction systems for the degradation of pollutants are explained. Recent work on plasmonic-based heterojunction photocatalysts for the degradation of various organic pollutants in wastewater such as dyes, pesticides, phenols, and antibiotics is discussed. Challenges and future developments are also described.

Fundamentals and Applications of Gold Nanoparticle-Based Plasmonic Photocatalysts for Water Purification

“…Also, the conclusion of the degradation mechanism under visible-light irradiation should be carefully drawn by taking the possibilities of the participation of the self-sensitization and plasmon-induced direct charge transfer other than the HET mechanism (Scheme b). From a viewpoint of material science to enhance the photocatalytic activity, the development of all-solid-state Z-scheme type plasmonic photocatalysts is highly expected due to the high redox ability of charge carriers generated by low-photon excitation and effective charge separation . Also, the overall efficiency in the plasmonic photocatalytic reactions is given by multiplication of the efficiencies of a series of the physical processes and the efficiency of the surface chemical reaction .…”

“…From a viewpoint of material science to enhance the photocatalytic activity, the development of all-solid-state Z-scheme type plasmonic photocatalysts is highly expected due to the high redox ability of charge carriers generated by low-photon excitation and effective charge separation. 24 Also, the overall efficiency in the plasmonic photocatalytic reactions is given by multiplication of the efficiencies of a series of the physical processes and the efficiency of the surface chemical reaction. 40 Thus, the specification of the detailed information about the oxidation sites and the modification by the promoters can be important subjects for further improving the photocatalytic activity.…”

“…However, TiO 2 responds only to UV light accounting for only about 3% of the solar energy. Recently, plasmonic photocatalysts consisting of gold NPs and semiconductors (Au/SCs) have attracted a great deal of attention due to the wide spectral responsiveness from visible to near-infrared (NIR). − Since the first report by Garcia and co-workers, research on the environmental purification by the Au/SC plasmonic photocatalysts represented by Au/TiO 2 has been vigorously continued, and comprehensive review papers including on the topic have been published. − However, review papers specializing in plasmonic photocatalyzed water purification are only limited. − At the present stage, we believe that it is important to manifest the material design guidelines of plasmonic photocatalysts for water purification by taking the similarity and difference with that for the usual solar-to-chemical transformations to accelerate future research in this field.…”

Internal conversion induced by external electric and magnetic fields

“…The interaction of electromagnetic fields with matter at the molecular level is one of the main tasks in photophysical studies 1–7 since the knowledge of the energies of electronic states and their lifetime are important for understanding molecular luminescence properties. 8–10 The energy of excited states can at low molecular concentration be converted to vibrational energy of lower-lying states by nonradiative transitions and to light by radiative intramolecular electronic transitions.…”

Influence of plasmons on the luminescence properties of solvatochromic merocyanine dyes with different solvatochromism

“…Improvements of the light conversion in photocatalytic and photovoltaic systems can be obtained by a direct transfer of hot charge carriers 21–23 and by increasing the absorption rate constant of photons by the reactant molecules due to the optical amplification of the local electromagnetic field at the NP surface. 24,25 These properties are used to increase the rate of chemical reactions such as water splitting, 25,26 CO 2 recovery and utilization, 27 photodegradation of organic compounds 28–30 as well as to increase the efficiency of photocatalytic materials 25,31,32 and solar cells. 33–37…”